1. Field of the Invention
This invention relates generally to anti-torque thruster systems. In particular, the present invention relates to an emergency anti-torque thruster system.
2. Description of Related Art
Helicopters and other rotary-wing aircraft are typically lifted and propelled by one or more large horizontal rotors, each comprising multiple, angled or angleable, rotor blades. Helicopters are able to fly because forward motion of the angled rotor blades forces air downwards, creating lift, which forces the rotor blades, and, in turn, the helicopter suspended beneath, upwards.
Useful flight requires that the helicopter's altitude, yaw (movement in the right-left horizontal direction), pitch (tilting forward and back), and roll (tilting sideways) be controlled simultaneously. For yaw control, the pitch, or angle-of-attack, of the helicopter's tail rotor blades is typically varied to alter the amount of thrust produced, thereby altering the right-left horizontal direction of the helicopter. For dual rotor helicopters, a differential between the two rotor transmissions is typically adjusted to transmit differential torque to each rotor and thus turn the helicopter. Yaw controls are usually operated with anti-torque pedals. For pitch or roll control, the angle-of-attack of the main rotor is altered.
The collective pitch control lever, which is typically positioned at the pilot's left side, is a helicopter's primary altitude and power control. The collective is used to vary the lift produced by the main rotor system by increasing or decreasing the pitch, or angle-of-attack, of all the helicopter's main rotor blades simultaneously or collectively throughout the 360-degree plane-of-rotation of the main rotor.
When the collective is raised, the angle-of-attack of the blades is increased, and the main rotor system produces more lift. When the collective is lowered, the angle-of-attack of the blades is decreased, and the main rotor system produces less lift. Increasing the collective and adding power with the throttle cause the helicopter to rise.
The throttle is usually a twist grip mounted at the end of the collective and is used to control the absolute power produced by the engine, which is connected to the rotor by a transmission. On a piston-powered helicopter, the pilot must manipulate the throttle to maintain rotor RPM as the pilot increases and decreases the collective. On a turbine-powered helicopter, a servo-feedback loop between the engine fuel control unit and the governor automatically adjusts the power turbine to maintain rotor RPM as the pilot increases and decreases the collective. Thus, on a turbine-powered helicopter, the pilot normally sets and leaves the throttle at 100 percent power during flight and the servo-feedback loop in the helicopter's engine controls relieves the pilot of routine responsibility for controlling the maintain rotor RPM.
The cyclic controls the pitch of the helicopter's blades cyclically, causing the lift to vary across the plane of the rotor disk. This is how the pilot causes the rotor system to tilt, and the helicopter to move above the ground. In a hover, moving the cyclic forward, for example, makes the helicopter fly forward. Moving the cyclic to the left, for example, makes the helicopter translate, or move over the ground, to the left, and so forth. In flight, the cyclic is the primary airspeed control. Applying forward cyclic causes airspeed to increase. Aft cyclic pressure reduces airspeed. The cyclic is usually controlled by the stick in front of the pilot.
Turning the rotor generates lift but it also applies torque to the body of the helicopter. The torque tends to spin the helicopter in the opposite direction of the rotation of the rotor.
Various methods for counteracting the effects of the torque have been devised. The most common method of counteracting torque is through the use of a smaller, substantially vertical tail rotor mounted at the rear of the helicopter's tail boom. Other methods include the use of a NOTAR® design, wherein air is forced through a long slot along the tail boom, utilizing the coanda effect to produce forces to counter the torque. Another alternative method for counteracting the torque is to utilize two large horizontal rotors that each turn in opposite directions. In this manner, the torque of each rotor counteracts the torque of the other. The anti-torque pedals are used by the pilot to compensate for the torque produced by the main rotor.